What Does Lactobacillus Reuteri Do?

Updated July 2026

This one's about what Lactobacillus reuteri actually does in the body, rather than which foods contain it, we've covered that separately in our dedicated food sources guide. Here's the mechanism, the genuinely researched benefits, and a few claims about it that don't hold up as well as they used to.

What does Lactobacillus reuteri actually do in the body?

Lactobacillus reuteri (you may also see it listed under its updated scientific name, Limosilactobacillus reuteri, following a 2020 reclassification) is a naturally occurring bacterium found in the human gut. It's able to survive the acidic environment of the stomach and temporarily establish itself along the digestive tract. Once there, it produces antimicrobial compounds, including organic acids, ethanol and a substance called reuterin, which can compete with less helpful bacteria for space and resources. A widely cited review on L. reuteri and human health describes this antimicrobial activity and its interaction with the immune system as its two main areas of established function.

What are the benefits of Lactobacillus reuteri?

The best-supported use is general digestive support, this is the strain most commonly associated with helping manage certain types of diarrhoea and general gastrointestinal discomfort, though WebMD notes that even here, "its benefits are not well defined" across the board, so it's worth treating as generally supportive rather than a guaranteed fix.

The single most specifically researched use is infantile colic, and research on probiotics tends to be specific to the particular product studied rather than applying evenly across L. reuteri as a whole. Research summarised by Examine.com describes certain L. reuteri products as appearing to improve symptoms of colic in infants, alongside broader use for various gastrointestinal issues. If you're considering this for a baby, it's worth discussing the specific product with a GP or health visitor rather than choosing one based on the species name alone.

Beyond digestion, there's genuine ongoing research into L. reuteri's role in regulating immune responses and reducing inflammation, described in a 2025 review of its effects on oral and systemic health. This is a real and active area of study, not settled science, and "probiotic" doesn't carry an approved health claim in the UK or EU, so we're describing research direction rather than promising an outcome.

A couple of claims you'll see repeated elsewhere are worth being honest about rather than repeating uncritically. Cholesterol-lowering and H. pylori elimination both get mentioned in older or less rigorous sources, but the evidence behind both is limited and inconsistent, not something we'd present as an established benefit. Similarly, some combination probiotic products are marketed for eczema, but results across studies have been mixed rather than a clear, consistent win.

Does Lactobacillus reuteri have any side effects?

Generally, it's considered safe and well tolerated for most people. Mild bloating, gas or general digestive discomfort can happen, particularly in the first few days of starting, and usually settles as your gut adjusts. As with any live bacterial supplement, anyone with a significantly weakened immune system, a central venous catheter or feeding line, or a serious ongoing illness should check with a doctor before starting, since rare cases of bloodstream infection from live bacterial products have been documented in these higher-risk groups.

How long does it take for L. reuteri to work?

This depends a lot on what you're taking it for, and it's more variable than a fixed "3 to 4 days" figure some sources quote. Digestive symptoms are sometimes noticed within the first week or two of consistent use, but for some purposes, ongoing gut and immune support, for instance, benefits build gradually over several weeks rather than arriving on a fixed schedule. We've gone into UK probiotic timing more broadly, including what genuinely speeds things up and what doesn't, in this article.

How can you get more Lactobacillus reuteri?

Through a specific, labelled supplement is the most reliable way, since you can't tell which bacterial strains are present in a food just by looking at it. Certain fermented foods and specialist yoghurts are also a source, though not every fermented product contains this specific species. We've broken down exactly which foods, brands and home methods actually contain L. reuteri, with amounts and practical detail, in our food sources guide, so we won't repeat the full list here.

Quick questions, quick answers

Is Lactobacillus reuteri the same as other probiotic strains?
No. Research on probiotics tends to be specific to the particular product studied, so findings about L. reuteri don't automatically apply to other Lactobacillus species, and different L. reuteri products are studied for different specific uses.

Can children take Lactobacillus reuteri?
It's commonly used in children's products, and certain L. reuteri products have been researched for infant colic specifically. Always check with a GP, pharmacist or health visitor before giving any probiotic to a baby or young child.

Is Lactobacillus reuteri good for skin?
The evidence here is limited and inconsistent rather than well established, so we'd treat any skin-specific claim with caution until better-quality research is available.

None of this is medical advice. If you're taking regular medication, managing an ongoing health condition, or unsure whether a probiotic is right for you, a pharmacist or GP can advise based on your situation.

Got more questions about probiotics or gut health? Have a browse of the rest of our Health Insiders blog, or send us a message on Instagram.